In recent years, the development in higher integration, higher performance, and higher density packaging of semiconductors for use in electronic devices, communication instruments, personal computers, and the like has been progressively accelerated. Consequently, a laminate having excellent properties such as heat resistance and low water absorption properties is required as a metal foil clad laminate for use in a printed wiring board. Conventionally, FR-4 type laminates made of epoxy resin cured by dicyandiamide are widely used as a laminate for use in a printed wiring board. The recent requirement for high heat resistance, however, is beyond the limit of performance of the laminates of this type.
On the other hand, cyanate ester resins are known as resins for use in a printed wiring board, having excellent heat resistance. Recently, a resin composition obtained by, for example, mixing a bisphenol A-based cyanate ester resin with other thermosetting resins or other thermoplastic resins has widely been used as a resin composition for high functional printed wiring boards for semiconductor plastic packages and the like. Although the bisphenol A-based cyanate ester resin is excellent in electrical properties, mechanical properties, chemical resistance, adhesion, and the like, water absorption properties and heat resistance after moisture absorption under severe conditions are insufficient in some cases. The development of cyanate ester resins having other structures is, therefore, under way for further improvement in properties.
With the development in higher integration, higher performance, and higher density packaging of semiconductors, the high heat dissipation properties of a printed wiring board has been emphasized. A laminate having high heat resistance, low water absorption properties, and high thermal conductivity is, therefore, needed. For example, a resin composition containing a cyanate ester resin (A) having a specific structure, a non-halogen epoxy resin (B), and an inorganic filler (C) as essential components has been proposed as a flame-retardant resin composition for a halogen-free laminate having improved curability, water absorption rate, heat resistance after moisture absorption, and insulation reliability (refer to Patent literature 1).
Further, an electrically insulating resin composition having improved thermal conductivity with a large amount of inorganic filler having a specific particle size distribution has been proposed (refer to Patent Literature 2).